OWINGS MILLS, Md. -- Baltimore Ravens tight end Darren Waller ran straight toward safety Kai Nacua at Saturday's practice before making a move that doubled as a reminder of his scintillating potential.

It was a one-on-one red zone route-running drill. Waller planted his left foot into the ground and made a sharp cut to his right to to shake free from Nacua, leaving the defender scrambling. Waller then hauled in an easy touchdown as Nacua flailed his arms at the pass, continuing his eye-opening performance during his first practice with the team since last spring.

In June 2017, the NFL handed Waller a year-long suspension for repeated violations of the league's substance abuse policy. He's admitted to smoking marijuana in the past.

And while Saturday brought signs that Waller still has the skills and fitness to contribute for the Ravens, coach John Harbaugh wasn't giddy to discuss that. He said his job was to push Waller, not to praise him.

"I haven't seen the guy for a year," Harbaugh said of Waller. "I love him. He's a great guy, talented guy and all that. But, where's he been? So, you have to be here. You don't just come waltzing in and all of the sudden you're the starting tight end. You have to prove it."

That's what Waller's aiming to do, but he's on a time crunch. The NFL reinstated the 2015 sixth-round pick earlier this week, and Waller suited up for the first time Saturday, leaving him exactly three weeks to impress coaches before the Ravens trim the roster from 90 players to 53.

There's stiff competition ahead of Waller. The Ravens took Hayden Hurst in the first round of April's draft and Mark Andrews in the third, while Nick Boyle, Maxx Williams and Vince Mayle all bring specific skill sets to the tight end competition.

Still, Waller offers unique ability. The former Georgia Tech wide receiver showed off his greatest strength Saturday during red zone drills when he used his 6-foot-6, 255-pound frame and natural quickness to break open for three touchdown receptions.

Those glimpses of promise don't guarantee Waller anything, though. After 14 months away from the Ravens, he has to relearn the playbook in short order to make the team.

"He's really, really been cramming," tight ends coach Greg Roman said. "He is cramming for a final exam right now, and [there's] not a lot of sleep going on. He's doing a very good job."

Plus, Waller has to get into shape. He's been working out, but it's difficult to replicate an NFL practice on an empty field with a personal trainer.

"You don't get in football shape without grinding through training camp," Roman said.

And even if Waller does master every offensive play and work himself into a peak physical condition, he'll still have a tough time earning a place on the 53-man roster. The numbers need to shake out in his favor.

For now, Waller attracts intrigue because of his history, his talent and his opportunity. He caught 10 passes for 85 yards and two touchdowns in 2016 and appeared likely to build on that campaign before he failed another drug test the next offseason.

Harbaugh isn't impressed with Waller yet and declined to evaluate the tight end's first practice. He wants to see him remain on the field for a little while first.

"Like I told him, I'm going to be the hardest guy on him of anybody," Harbaugh said. "I'm going to be on him every single day, because he has a lot to prove."